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Search: id:A070170
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| A070170 |
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Numbers n such that sigma(n-phi(n))=phi(n). |
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+0
2
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| 2, 15, 39, 255, 627, 939, 1431, 1581, 2409, 3459, 4797, 14289, 20619, 30987, 31935, 43791, 57291, 68991, 71193, 73749, 74841, 94671, 120669, 121227, 132297, 148161, 162843, 196449, 200787, 209451, 217191, 302907, 308937, 434733, 439959, 455961
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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All terms 2 < a(n) < 20000000 are odd and divisible by 3. Most are square-free.
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FORMULA
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From numerical observation if n>31 : ln(n)^10<a(n)<ln(n)^11.
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MATHEMATICA
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Do[s=DivisorSigma[1, (n-EulerPhi[n])]-EulerPhi[n]; If[Equal[s, 0], Print[n]], {n, 1, 2000000}] (PARI) for(n=2, 2000000, if(sigma(n-eulerphi(n))==eulerphi(n), print1(n, ", ")))
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CROSSREFS
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Cf. A070171.
Adjacent sequences: A070167 A070168 A070169 this_sequence A070171 A070172 A070173
Sequence in context: A064113 A007217 A070009 this_sequence A033568 A032016 A001007
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre and Elemer Labos, May 06 2002
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